Let's Make Robots!

Building a SpurtBot

It's a simple line follower.

Introduction

SPURT stands for School Project Using Robot Technology, a concept introduced by the Rostock University, in Germany. You can find more about their program on their website.

These instructions are for building a very simple version of a line following robot, based on the SpurtBot design above. Thanks to Hartmut from Rostock University for his support in creating this design.

The video explains a bit how the SpurtBot works, and shows it in operation. The version of the SpurtBot in the video is not identical to this one, but it is very close and works just the same. A couple of resistors were eliminated, which simplified the circuit for these instructions.

Here's the schematic for the circuit.

NOTE: I have found that adding a 10k ohm pull-down resistor between pin 1 of the QRD-1114 and ground improves performance.  It tends to make the line following more accurate in some situations by insuring the base of the BC337 transistor is pulled firmly to ground.

 

I hope you enjoy building your SpurtBot!

 

STEP 1: Gather your materials

Parts/Materials

  • (2) Bearings from inline skates (Search YouTube for vids on how to remove and clean them.), or you can order them.
  • (1) Balloon for Bands/tires (Use heavier duty 'punching balloon'.), I order them in bulk.
  • (1) Popsicle/craft stick (I like nice color ones, but use whatever you like.), I order them in bulk.
  • (1) 2 inch piece of 5/16 inch wooden dowel (The dowel should fit snugly into the bearings.), from your local hardware store.
  • (2) Motors (3VDC, Jency Motor ST130-12240-38, Jenco part # 154915 or Mabuchi FK-260SA-10400, Jenco part # 2081908)
  • (2) AA alkaline batteries
  • (1) QRD-1114 reflective sensor
  • (1) bc 337 NPN transistor
  • (1) Resistor (50 to 100 ohm for IR emitter)
  • (1) Battery holder for 2xAA batteries
  • 8 inches of red wire
  • 6 inches of white wire
  • 6 inches of black wire

Tools/Supplies

  • Wire cutters
  • Wire strippers
  • Needle nose pliers
  • Hot glue gun and glue sticks
  • Soldering iron and solder
  • Drill and 1/16 inch drill bit
  • Sharp scissors
  • Heat shrink tubing (1/16 inch, 3/32 inch, and 1/8 inch)
  • Butane Lighter or other heat source

 

STEP 2: Make some holes

Using the four leads of the QRD-1114 sensor as a guide, mark four dots near the very end of the craft stick.

Now use the three leads of the bc337 transistor to mark three dots about half an inch behind the dots for the QRD-1114.

The two sets of holes should be close enough to each other that the leads of the QRD-1114 when it is inserted can be bent back to make contact with the leads of the bc337 transistor.

Use a 1/16th inch drill bit to drill holes over each of the dots. Go slowly and be careful to avoid running the holes too close together. Use of a drill press is very helpful, but you can do it with a hand drill if you don’t have one. A wooden backer board underneath the craft stick will also help support the material while you are drilling.

When you are done, the craft stick should look a lot like the picture below.

 

STEP 3: Attach the dowel

Mark the center of the dowel as a guide, and use the hot glue gun to attach the dowel on top of the craft stick. The dowel should be about 3/5th back from the front of the craft stick where the holes are drilled.

You want to be sure the dowel is square with the craft stick. I like to use the corner of a table to hold the two pieces of wood at 90 degrees while the hot glue is drying. 

 

STEP 4: Attach the bearings

Next place one bearing flat on its side. Hold the craft stick and dowel so that one end of the dowel is directly over the hole in the bearing. Being careful not to apply any pressure to the craft stick, push down firmly on the other end of the dowel until it is inserted fully into the bearing.

The end of the dowel should be flush with the surface of the side of the bearing, as shown in the picture below.

Now repeat the process with the other bearing, so that you have one bearing on each side of the dowel. While you insert the second bearing, be careful to press down on the top of the dowel, rather than on the edges of the first bearing, or you might wind up with the dowel inserted too far into the first bearing.

Also be sure that the bearings are mounted at 90 degrees to the dowel. Congratulations, you now have a ‘rolling chassis’ for your SpurtBot.

 

STEP 5: Attach your motors

The motors need to be positioned carefully. Before you mount your motors, keep the following things in mind.

  • The motor shafts need to be parallel to the rolling surface of the bearings. In other words, the motor shafts should be at 90 degrees to the craft stick and parallel to the dowel.
  • The right motor shaft will need to be thickened with 3 to 4 pieces of heat shrink tubing. You need to leave about 1/8th of an inch between the shaft and the surface of the bearing to allow for the shrink tube to fit.
  • Despite the above, you don’t want too much space between the motor shaft and the bearing, because it will add too much tension to the wheel when the bands are installed.
  • To keep tension roughly equal on both bearings, you want both motors positioned the same distance from the bearings.
    The shaft of the right motor should be positioned directly behind the right bearing. The shaft of the left motor should be positioned directly in front of the left bearing.
  • The shaft should overlap both sides of the bearing a little bit, so the tension bands will stay on the wheels.

OK, time to glue the motors on! Don’t sweat the points above too much. If you mess it up, hot glue is easy to remove and you can try again.

Start with the right motor, which will be mounted to the rear of the dowel. Position the motor and get a good feel for where it will go, noting the points above. Once you are ready, place a generous amount of hot glue on the craft stick and the dowel on the side the motor will touch.

CAUTION: Hot glue is, well… HOT. It will stick to your skin and burn you. The end of the hot glue gun is very hot. Don’t touch it, and don’t let it touch anything that can burn.

Pull the hot glue gun away quickly, and place it safely on the table. Working quickly, grab the right motor and place it on the SpurtBot. You will have a few moments as the glue hardens, so check that the shaft is positioned as you want it. Then hold it still for a minute while the glue dries.

After the glue is dry, you can break off the little annoying threads of hot glue that inevitably happen.

If you are happy with the way your right motor was mounted, repeat the procedure with the left motor. Remember that the left motor will be mounted in front of the dowel, with the shaft facing the left side of the robot.

 

STEP 6: Mark your connections

I like to mark all of my connections, so I don’t make (many) mistakes. Look at the SpurtBot from the top so that the front end with the holes is facing away from you.

Start with the four holes you drilled in Step 2 for the QRD-1114. Carefully mark the front-left hole with a ‘1’. Moving clockwise, the front-right hole is marked ‘2’. The hole just below that is marked ‘3’, and the hole just to the left of that is marked ‘4’.

Next, we’ll mark the three holes for the bc337 transistor. The left hole is marked ‘e’ for emitter. The center hole is marked ‘b’ for base. The right hole is marked ‘c’ for collector.

I also like to mark the shape of the bc337 transistor right on the SpurtBot, so I always insert it the right way. Make a little ‘D’ shaped marking behind the three mounting holes, with the flat side of the ‘D’ facing the front of the SpurtBot.

 

STEP 7: Install the QRD-1114

Look at the QRD-1114 reflective sensor. Pin 1 of the sensor is marked with a dot on the case. The sensor will be mounted ‘dead bug’, meaning the sensor will be pointed down with its leads up in the air.

You will insert the leads up from the bottom, and through the four holes you drilled in the front of the SpurtBot in Step 2.

Make sure that lead 1 of the QRD-1114 is inserted into the hole you marked ‘1’.

Hold the QRD-1114 flush against the underside of the SpurtBot, and bend all four leads slightly outward to help hold the sensor in place.

 

STEP 8: Install the resistor

You are going to solder the resistor between pins 1 and three of the QRD-1114. A small 1/8th Watt resistor should fit nicely. Try to solder it so that it is as close to the craft stick as possible. This will help keep the QRD-1114 in place.

Solder one side of the resistor to pin 1 of the QRD-1114. It may be helpful to use an object to hold the other side of the resistor, or get a friend to help you. Don’t worry if the solder isn’t perfect.

Now go solder the other side of the resistor to pin 3 of the QRD-1114. Because the resistor is now held in place from your previous solder joint, this should be pretty easy.

If you need to, go back and re-solder the first side of the resistor, positioning it so that it is close to the surface of the craft stick, as mentioned above.

Check to be sure the QRD-1114 is still mounted flush to the underside of the craft stick. Adjust the two solder joints if needed to be sure the QRD-1114 is in place.

Cut off the leads from the QRD-1114 and the resistor at pin 3 only. Leave the leads of the QRD-1114 pin 1, 2 and 4 alone for now.

NOTE: If you want to use the optional 10k ohm pull-down resistor, this would be a good time to install it. Solder the resistor across pin 2 and pin 4 of the QRD-1114, so that the 10k ohm resistor is sitting diagonally across the resistor you already installed between pin 1 and pin 3. Then cut the excess leads from the 10k ohm resistor, leaving the excess lead from the QRD-1114 pin 2 and pin 4 in place for now. Be careful not to short any of the QRD-1114 pins.


STEP 9: Test your motors

You need to know which way your motors will turn when you connect power to them. So we are going to test them.

Insert the two AA batteries into the battery holder.

Start with the right motor, which is mounted behind the dowel with its shaft behind the right bearing.

Looked at from the right side, the bearing needs to turn clockwise for the SpurtBot to move forward. Since the motor will be attached to the bearing directly using a band, the right wheel motor also needs to turn clockwise.

 

Temporarily attach the black wire from the battery holder to one lead of the motor and the red lead from the battery holder to the other lead of the motor. Note which way it is spinning when viewed from the right side of the robot.

If it is spinning clockwise, mark the motor lead attached to the red wire with a ‘+’ and the motor lead attached to the black wire with a ‘-’.

If the motor is turning counter-clockwise, then you need to reverse the markings. Mark the motor lead attached to the red wire with a ‘-’, and mark the motor lead attached to the black wire with a ‘+’.

Now test the left motor. Repeat the above procedure, making sure the motor will turn counter-clockwise when viewed from the left side when you attach the battery leads.

Take your time with this step. As they say in carpentry, “Measure twice, cut once.”

 

STEP 10: Connect the red wires

Carefully strip about ¼ inch of insulation from one end of the red wire. Pinch the exposed conductors at the end of the wire between your thumb and forefinger, and twist the wire several times. This will help keep the individual conductors together while you work with them.

In the following steps, I will refer to this technique as ‘twisting the leads’. You’ll use this technique whenever you strip some insulation from the wire.

Next, use a clamp or other method to hold the exposed end of the red wire above your work surface, and tin the lead with your soldering iron. Use the smallest amount of solder you can. If you do not know how to tin your leads, look it up on the Internet or ask for help.

Now take the tinned end of the wire, and bend a little hook in it with the needle nose pliers.

 

Wrap the hook of wire around pin 1 of the QRD-1114, and solder it in place. Be sure that the resistor is still soldered properly to pin 1 too.

You may now cut the extra leads of the resistor and QRD-1114 from pin 1 only. Leave the leads of the QRD-1114 pin 2 and 4 alone for now.

 

Route the red wire back along the body of the SpurtBot toward the left motor. Avoid covering any of the holes or markings for the bc337 transistor.

Check the length you need to reach the ‘+’ lead of the left motor. Leave an extra ¼ inch and then cut the red wire. Strip about 1/8 inch from the end of the red wire, and ‘twist the leads’.

Insert the twisted end of the red wire through the left motor contact for the ‘+’ lead, but don’t solder it yet

Now take the remaining piece of red wire that you cut off earlier. Strip about 1/8 inch from the end and twist the leads.

Take the twisted end of this red wire and insert it into the same left motor ‘+’ lead as the other wire. It may be a tight fit. Get creative, but be sure you will have good electrical contact. Now solder both red wires to the left motor ‘+’ lead.

 

Check your solder joint carefully. Be sure both wires are firmly connected.

Now route the free end of the red wire between the two motors, towards the ‘+’ lead of the right motor. Once again, cut the wire about ¼ inch longer than the length needed to reach the contact. Then strip 1/8 inch from the end of the wire, and twist the leads.

Insert the twisted end of the red wire through the ‘+’ contact of the right motor, but don’t solder it yet.

Cut a 3 inch piece of red wire from what you have left. Strip both sides and twist the leads.

Now insert one end of this red wire into the same ‘+’ contact of the right motor, where you have already inserted the red wire coming from the left motor. Again, it may be a tight fit.

Solder both leads firmly in place.

 

Use your soldering iron to tin the end of the red wire. Then use the needle nose pliers to bend a hook in the end of the wire.

 

STEP 11: Install the bc337 transistor

It’s time to install the transistor. Insert the transistor from the top of the SprutBot. Be sure to align the body of the transistors as it is marked. The flat side of the transistor should be facing the front of the SpurtBot.

The center pin should be in the hole marked ‘b’; this is the base of the transistor. The right pin should be in the hole marked ‘c’; this is the collector. The left pin should be in the hole marked ‘e’; this is the emitter.

Be sure to leave a little of the transistor leads showing at the top side of the SpurtBot. You will need to solder to the emitter lead from the top.
 

Turn the SpurtBot upside down, and bend the left and right leads of the bc337 transistor outward. This will help keep the transistor in place. Leave the center lead of the transistor (the base) standing straight.

 

Now, take the lead from pin 2 of the QRD-1114 and wrap it underneath the SpurtBot. Use the needle nose pliers to carefully route the lead so that it touches the base (center pin) of the transistor. Keep the lead as close to the underside of the SpurtBot as you can.

Be very careful that the base lead and the QRD-1114 pin 2 lead only touch each other and nothing else.

Next, solder the QRD-1114 pin 2 to the base of the transistor. Double check that you have a good connection, and that those two leads are not touching anything else.

Then cut the extra lead off the base of the transistor. It is important that none of the leads from the transistor end up longer than the body of the QRD-1114, or they will drag when the SpurtBot drives.

Turn the SpurtBot back over right side up. Bend the lead from the QRD-1114 pin 4 back along the body of the SpurtBot towards the emitter lead of the bc337 transistor. Use the needle nose pliers to position the QRD-1114 pin 4 lead against the emitter of the transistor.

 

Be very careful that the pin 4 lead of the QRD-1114 is touching the lead of the emitter and nothing else.

Carefully solder the pin 4 lead of the QRD-1114 to the emitter of the transistor. Double check that you have a good connection, and that those two leads are not touching anything else. It is easy to accidently short against the base of the transistor.

Trim the extra wire from the lead of the QRD-1114.

 

STEP 12: Connect the white wire

Strip about ¼ inch from the end of the white wire. Twist the leads. Then tin the leads with your soldering iron using as little solder as possible.

Bend a little hook in the tinned end of the wire using the needle nose pliers.

Now turn the SpurtBot upside down, and connect the hooked end of the white wire to the collector lead of the transistor. It is helpful to use the needle nose pliers to clamp the little hook shut onto the lead of the collector so it will stay in place while you work with it.

Be very careful that the white wire and the collector lead are not touching any other connections. 

Next, solder the white wire to the collector. Double check your connection.

 

Cut off the extra lead from the end of the collector.

Now route the white wire along the underside of the SpurtBot, towards the right motor. The wire will cross the body of the SpurtBot to come up near the ‘-’ lead of the right motor.

Cut the white wire about ¼ inch past the length it needs to reach the ‘-’ contact of the right motor. Strip about 1/8 inch of insulation from the end of the white wire, and twist the leads.

Insert the stripped and twisted end of the white wire into the ‘-’ contact of the right motor and solder it in place.

 

Press the white wire against the underside of the SpurtBot so it is flush. Hold it in place with a dab or two of hot glue.

 

STEP 13: Connect the black wire

Strip about 1/8 inch of insulation from the end of the black wire. Twist the leads. Tin the end with as little solder as possible.

Use the needle nose pliers to bend a little hook into the tinned end of the black wire.

Now turn the SpurtBot upside down, and connect the hooked end of the black wire to the emitter lead of the transistor. It is helpful to use the needle nose pliers to clamp the little hook shut onto the lead of the emitter so it will stay in place while you work with it.

Be very careful that the black wire and the emitter lead are not touching any other connections. 

Next, solder the black wire to the emitter. Double check your connection.

Cut off the extra lead from the end of the emitter.

Now route the black wire along the underside of the SpurtBot, towards the left motor. The wire will cross the body of the SpurtBot to come up near the ‘-’ lead of the left motor.

Cut the black wire about ¼ inch past the length it needs to reach the ‘-’ contact of the left motor. Strip about 1/8 inch of insulation from the end of the black wire, and twist the leads.

 

Insert the stripped and twisted end of the black wire into the ‘-’ contact of the left motor, but don’t solder it yet.

Remove the batteries from the battery holder. Strip and twist the end of the wires if they are not already so prepared.

Insert the black lead from the battery holder into the same left motor ‘-’ contact as you previously inserted the black wire from the transistor emitter. Once again, this may be a tight fit.

 

Solder both black wires to the ‘-’ contact of the left motor. Be sure you have a good connection to both wires.

Press the black wire leading to the transistor emitter against the underside of the SpurtBot so it is flush. Hold it in place with a dab or two of hot glue.

Route the black wire leading to the battery holder between the two motors.

If the red lead of the battery holder is not already stripped, twisted and tinned, do so now. Use the needle nose pliers to put a little hook in the end of the wire. You will use this hook and the hook on the end of the other red wire to connect the battery to the SpurtBot.

 

STEP 14: Quick motor test

We are getting close now. Time for a quick test to be sure we’ve got it all right so far.

Insert the two AA batteries into the motor case. Take the SpurtBot to a location with good lighting and have something with a bright white and dark black surface to test against.

Connect the hooked red wire from the battery holder to the hooked red wire coming from the ‘+’ contact of the right motor. The left motor should start to spin counter-clockwise when viewed from the left side of the SpurtBot.

Note that the wheels themselves will not spin, because we haven’t connected the traction bands yet. You can feel which way the motor is spinning by touching the shaft with your finger.

The right motor may not be spinning, which is fine. Place the SpurtBot on a bright white, well-lit surface. The right motor should now spin clockwise as viewed from the right side of the SpurtBot.

Place the SpurtBot on a black surface. The right motor should immediately stop spinning, while the left motor continues to spin.

If all works as described above, great! Move on to the next step.

If there’s a problem, check everything and test again.

 

STEP 15: Attach the battery holder

Now you can hot glue the battery holder to the top of the motors. Make sure to place the battery holder with the wires to the rear of the SpurtBot.

 

Place the battery holder as far forward as you can. This will keep the weight to the front of the SpurtBot, so the sensor maintains contact with the surface that it drives on. The battery holder should be balanced left to right along the central axis of the SpurtBot.

 

STEP 16: Cut the traction bands

Using a pair of sharp scissors, cut the ridged edge from the neck of the balloon.
Now cut two bands from the end of the neck, about the width of the bearings. Try to keep the cuts nice and straight.

 

You can fit the traction band onto the left bearing and motor shaft now. Start by stretching one band over the bearing on the opposite side from the motor shaft. Extend the band around the motor shaft.

Now carefully rotate the bearing. The band should tend to align itself onto the bearing and motor shaft.

 

STEP 17: Thicken the right motor shaft

The right wheel needs to spin faster than the left when it is running. Because there is a small voltage drop across the transistor, the voltage applied to the right motor will always be a bit less than the left, which is connected directly to the battery.

However, by thickening the right motor’s shaft, we change the ratio of the diameters of the bearing and the shaft. Effectively, you are changing the gear ratio. This will make the right motor spin faster. It will also have a little less torque, but it will be enough to move the SpurtBot, so that is OK.

 

Find the smallest size shrink wrap tube you can fit over the right motor shaft. Measure a length that is just a tiny bit shorter than the length of the motor shaft, and cut the tubing with a pair of sharp scissors. Make your cut nice and square.

Place the cut tubing over the end of the right motor shaft.

Now you are going to use a lighter or other heat source to shrink the tubing. You should be very careful not to burn yourself, or to melt any parts of the Spurtbot.

Bend all wires out of the way. Think about where the flame of the lighter will go, and be careful not to melt the battery holder, bearing or anything except the shrink tubing.

 

Hold the SpurtBot in one hand, and apply the flame from the lighter briefly to the shrink tubing. It is better to apply the heat for a short time, and then go back a few times than it is to keep it on a long time.

Allow the shrink tubing to cool, then rotate the shaft 180 degrees and apply heat again. You should now have a nice tight fit.

 

Now find the smallest size shrink tubing that will fit over the last layer of tubing. Cut it to size and shrink it as before. You will need 3-4 layers of tubing. You may be able to use the same size tubing more than once, depending on how much it shrinks. Check for the right size each time.

It is a good idea to test the SpurtBot once you have 3 layers of shrink tubing. You can always put another layer on later if you need it, but they are difficult to remove.

 

Once you have 3 layers on the shaft of the motor and the shrink tubing is cool, you can install the traction band the same way you did for the left motor. Then got to the next step and test the SpurtBot. If it doesn’t turn right fast enough and stay close to the line, add another layer.

 

STEP 18: Testing your SpurtBot

Use a bright white surface with black electrical tape to make lines in a closed loop shape. You may need 2-3 widths of black tape to give your SpurtBot enough time to react to the sensor.

Start by testing inside the l. Set the SpurtBot inside the circle so that it will move around the loop in a clockwise direction. When the sensor is on the black, the right motor will stop, and the SpurtBot will turn to the right. Now the sensor will cross over to the white background, and the right motor will spin faster than the left, turning the SpurtBot back towards the black line.

It should follow the line pretty closely, but may cut some tight corners.

Now place the SpurtBot on the outside edge of the black loop, facing so it will go around counter-clockwise. Once again, when the sensor is on the black, the right motor turns off and the SpurtBot begins to turn away from the loop. As soon as it hits the white background the right motor spins faster than the left, and the SpurtBot should turn back towards the line. If it follows the line pretty closely, all is well. If it doesn’t turn quite fast enough, try going back to Step 17 and adding one more layer of shrink tubing.

As you add layers, the right motor spins faster, but you are also reducing torque. If you add too many layers, the right motor may not have enough torque to move the SpurtBot.

Have fun!

 

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Hello,

this is a very nice project, thanks!

I'm looking into building a line follower with kids and I'm currious if I could replace the sensor with LED and LDR - and perhaps a darlington pair?

My electronics-fu is a little rusty, I've seen ALF and other analog line follower online, but I'd like to use a one-motor-controll solution. The sensor seems to be hard to source here, plus I would like to decrease the cost so the students can take it home, too.

 

 

Hi Schorhr, I cannot recommend to use an LDR. I myself have done so as you can see on this page: http://spurt.pbworks.com/w/page/9145781/Simpelmobil

But I have found that it is very intricate to adjust ambient light in a way the robot can work on. I would not try it again - its mere an art than science. So I strongly recommend to use a reflective sensor sliding on the table surface way.

Cheers  --  Hartmut

Hello Hartmut,

thank you for the link and the information!

That does sound frustrating :-) Though It would only be a small project with a limited time frame (~1 hour), as long as it somewhat works... ;-)

The circuit of the Simpelmobil is exactly what I had in mind. Perhaps with a poti, darlington, if required, or let the students modify it and build a version with a different sensor later..

I will see if I have components here that are suited and try it anyway, and see how it performs. Would a LED be a simple method to enhance contrast and improve performance in difficult lighting conditions?

If it won't work at all I'll take your advice and build something different with them. As they have no experience with electronics I am trying to keep it as simple as possible.

Danke & Gruß,

Marcus

 

 

Hello Marc, I would suggest proceeding in three levels:

First (simplest): http://www.imd.uni-rostock.de/spurt/doc/spurt-53.htm Try several light receivers to start/stop a motor, E.g. LDR, photodiode, phototransistor etc. Even a LED together with a darlington might work since each LED also works as a light receiver (a bit less efficient than a photodiode). You also can try a solar cell from an old pocket calculator. A tiny bit tape glued at the motor axis lets you better whatch its spinning. With enough bright light and enough dark shadow it wil be possible in most cases to start/stop the motor by brightness intensity.

Second: Instead of bright sunlight from the window and dark shadow try pointing at several bright or dark surfaces whether it is possible to start/stop the motor. You will find that there are different grades of brighness and darkness which our human eye does not detect in the same way as the "electronic eye". So you will find some devices that work in the desired way.

Third: Now you need to find a motor which is suited to drive a mobile. This might be harder than it sounds. You need a motor with low current, low speed, high torque, long enough axis (more than 10 milimeters) and possibly not too much voltage need. You will find dozens of motors which will not work in the desired way. Andrew Terranova's description tells which motor will work.

I wish you good luck for all your tries. Maybe you can report something on facebook: https://www.facebook.com/pages/Spurt-Wettbewerb/341657232527946

Cheers  --  Hartmut

 

 

Hello Hartmut,
thank you again for all the advice, I really apreceate it!

Yes, I have build such circuits when I was younger (such as the LED as light detector), unfortunately I still have not unpacked all electronics stuff after moving to a new apartment :-) I hope I can digg through my stuff this weekend and build something.

The quest for cheap and suited motors is what is next, I am currently looking into the pager/iphone vibration motors as they are commonly available and very cheap (0,22 Euro / ~0,30 US Dollars), so I could make a inexpensie kit they could take home for free.
They aren't that powerful and usualy high RPM I think (sometimes used in tiny rc planes), an alternative would be modding a servo perhaps.
I have one of the small motors somewhere, and a 3d printer in case I need to print a gear drive, though I hope I can make the stuff with household items ;-)

But it's all not very critical. Even if the "robot" just whizzes through the room the (young) kids will probably have a blast anyway.

I'm still digging through Aliexpress, where some LDR cost 3 Cent each (including shipping, under the tax/duty-free value). But I have no clue about what components will work, so I'll buy a few of that type locally until I have a working prototype.

 Have a nice weekend!

 

Hello again,

if you just want a toy for the kids you could try a look at this model I built: http://www.rn-wissen.de/index.php/Beam#Eine_Art_Chaos-K.C3.A4fer

You can decorate the upper side of the CD with a nice animal picture (Chaos Beetle)

You need to protect the screws with some rubber sleeve for they don't scratch your floor.

Cheers   --  Hartmut

Hello Hartmut,

most of the components I ordered arrived.

The cellphone vibration motors are weaker then I expected and the weight is impossible to remove even though I searched for some tutorials before ordering them. I tried pinching them off and squeezing the weight appart, the only thing left to try is to hammer the shaft out of the weight, but   the thin nails I had here where all too soft :-/

The transistor and LDR with the bc337-25 seem to do the job nicely, changing the motor speed from very slow to fast.
I use these LDR for now, http://www.aliexpress.com/snapshot/6020160679.html

I found a cheaper source for motors that seem to be like the one I had here to play around with,
http://www.aliexpress.com/item/20pcs-lot-original-Vibrator-Vibration-Motor-for-iPhone-5-5G-motor-free-shipping/1667649192.html
but I do not want to run into similar problems again...
These cost 30 eurocent in larger quantity, http://www.neuhold-elektronik.at/catshop/product_info.php?cPath=96_97&products_id=4807 - but also draw a lot more current so I am not sure if I can use  the ordered components...

Any advice on alternatives, easy to source and inexpensive motors?
I have a few old computers with CD drives at hand, but not enough to provide motors to a whole class.

 

I also ordered a few other components such as http://www.aliexpress.com/snapshot/6028924819.html and http://www.aliexpress.com/snapshot/6020160673.html so hopefully something works out...

-Marcus

Hi Marcus, my quick & dirty answer (since I never tried out your devices):

I would not have had the courage to think about vibration motors. But since you have them now maybe you can try to use them as they are. Vibration would not harm much the traction I argue. Maybe you can try to reduce the vibration a bit by using abrasive paper to grind the vibration mass as much as possible while the axis is spinning at high speed. - No idea whether it helps

Concerning the TCRT5000 you need to try out whether it can discriminate between white and black paper. In infrared it could be fairly a similar reflection. And maybe you need to remove or at least shorten the separator between LED and photor transistor to ensure that reflected light can reach the receiving photo transistor.

If you want to use a rubber belt from motor axis to a ball bearing (wheel) for traction you must ensure that both axises are strictly parallel since otherwise the rubber belt would slip off.

Are you sure that your motors need less than 100 mA? Otherwise you need other transistors, those which tolerate higher collector current.

Good luck  --  Hartmut

 

 

Hello Hartmut,
the current motors are too weak to attach anything to the shaft - even the rubber band.  With the weight they bounce around too much... If I could just find an easy way to remove those things, I could let it drive directly on the shaft.
I have had another idea I am going to try out tomorrow, hopefully it will not damage the motor.
..
Right now the motor will almost stop if held close to a dark surface while spinning fast over wooden laminate flooring. Just with room light. Suprisingly.

The motors are tiny, sadly even smaller then the one I had before ordering these - I find different specifications from different sellers, but they should be a fair amount under 100mA. The BC337-20 still work and do not get hot either, not even when I use three cells.

Hi Marcus, please let me repeat it: You need a motor with high torque, low speed, low current, long shaft.

Andrew and I myself have tried out lots and lots of motors. You can choose either to select one of those we found or you can try to find another one, but be aware that it can take you weeks and bucks a lot. So we did. :-)

Good luck  --  Hartmut